Re: [RFC 1/3] tcp: randomize tcp timestamp offsets for each connection

On Thu, 2016-08-18 at 14:48 +0200, Florian Westphal wrote:

commit ceaa1fef65a7c2e ("tcp: adding a per-socket timestamp offset")
added the main infrastructure that is needed for per-connection
randomization, in particular writing/reading the on-wire tcp header
format takes the offset into account so rest of stack can use normal
tcp_time_stamp (jiffies).

So only two items are left:
 - add a tsoffset for request sockets
 - extend the tcp isn generator to also return another 32bit number
 in addition to the ISN.

Re-use of ISN generator also means timestamps are still monotonically
increasing for same connection quadruple.

Signed-off-by: Florian Westphal <fw@strlen.de>
---
 include/linux/tcp.h      |  1 +
 include/net/secure_seq.h | 13 +++++++++----
 include/net/tcp.h        |  2 +-
 net/core/secure_seq.c    | 19 +++++++++++++------
 net/ipv4/syncookies.c    |  1 +
 net/ipv4/tcp_input.c     |  7 ++++++-
 net/ipv4/tcp_ipv4.c      | 30 ++++++++++++++++++++----------
 net/ipv4/tcp_minisocks.c |  4 +++-
 net/ipv4/tcp_output.c    |  2 +-
 net/ipv6/syncookies.c    |  1 +
 net/ipv6/tcp_ipv6.c      | 28 ++++++++++++++++++----------
 11 files changed, 74 insertions(+), 34 deletions(-)

It seems tcp_v4_reqsk_send_ack() and tcp_v6_reqsk_send_ack() were not
taken into account.

See commit 20a2b49fc5385 changelog
packetdrill test showing the possible issue if the TS sent on an ACK in
SYN_RECV state is wrong.